Process facilities typically include tanks for the storage of liquid or granular materials. For example, at a petroleum or chemical refinery, tanks are used to store liquid feedstock such as crude oil and liquid products such as gasoline, diesel fuel and liquefied gasses. The tanks are typically large structures that can be 30 to 60 feet high. A liquid level gauge is typically mounted to the top surface of the tank (or nozzle) to measure the level of liquid material in the tank. The liquid level gauge generally has a display screen which can be read by an operator after climbing to the top of the tank. If the volume of the tank is known, the volume of material in the tank can be calculated from the measured level.